Grease compositions using a diurea compound as a thickener have been proposed so far. For example, JP 61-155496 A discloses a grease composition using, as a thickener, a diurea compound obtained by allowing an amine mixture comprising alkylphenylamine, an alkyl moiety of which has 8 to 16 carbon atoms, and cyclohexylamine in a molar ratio of 1:9 to 9:1, to react with a diisocyanate compound.